This invention relates to a quadrupole mass spectrometer.
In quadrupole mass spectrometers, one of the important factors that determine the capacity and performance of the instrument is the fringing electric fields produced at the entrance and exit ends of the quadrupole. The fringing fields exert a serious defocusing effect on the ion beam which enters or emerges from the quadrupole so that the ion transmission efficiency and consequently the sensitivity of the instrument are greatly reduced.
There is known a quadrupole mass spectrometer wherein the quadrupole and the ion detector are so arranged that the central axis of the ion detector is not in alignment with but off the central axis of the quadrupole. The "off-axis" arrangement helps prevent the light, X-ray, etc. produced by the ion source from entering the ion detector thereby to produce noise.